1. Field of the Invention
The present invention relates to a generator system for use in an automotive vehicle, and more particularly to a system for detecting malfunction in a clutch, through which a rotational torque of an engine is transmitted to an alternator.
2. Description of Related Art
Recently, an alternator having a higher capacity is used in an automotive generator system because a larger electric power is required to operate various kinds of electric or electronic devices mounted on an automotive vehicle. Accordingly, an inertial moment of a rotor used in the alternator becomes large. On the other hand, an idling speed of the engine is set to a lower level to reduce unnecessary fuel consumption.
For various reasons including those mentioned above, a rotational speed of the alternator rotor in a recent generator system tends to vary in response to engine strokes. That is, a tension of a driving belt that transmits a rotational torque of the engine to the alternator rotor varies in response to the engine strokes. This causes a problem that a life of the driving belt is shortened, especially in a generator system for a diesel engine.
To cope with this problem, JP-A-61-228153 proposes to use a one-way clutch in an alternator pulley that is coupled to a crankshaft pulley of an engine through a driving belt. If the alternator is directly coupled to the crankshaft pulley through the driving belt without using the one-way clutch, the engine torque is transmitted to the alternator when the engine speed is increasing while the inertial torque of the alternator is transmitted to the engine when the engine speed is decreasing. Therefore, a driving tension is imposed alternately on one side and the other side of the driving belt according to changes in the engine speed. If the alternator is coupled to the engine through the one-way clutch, the engine torque is transmitted to the alternator while the inertial torque of the alternator is not transmitted to the engine. Therefore, the belt tension variations are suppressed by using the one-way clutch.
The one-way clutch is composed of an inner ring connected to the rotor of the alternator, an outer ring coupled to the crankshaft pulley through the driving belt, and sprags or rollers interposed between the inner and outer rings. A high mechanical stress is imposed on the one-way clutch because the one-way clutch is frequently switched between its ON and OFF states. Further, it is used under severe environmental conditions, e.g., at a temperature changing in a wide range and under high vibrations of the engine or the vehicle. The one-way clutch has to be designed to endure the high mechanical stress and the severe environmental conditions. It is difficult to make the one-way clutch compact in size while assuring its high reliability. It is also possible to use another type of clutch composed of a torsion spring and clutch shoes. In this type of clutch, however, shoe powders generated by abrasion may cause malfunction of the clutch.
It has become clear that most of malfunctions of the one-way clutch are caused by locking between the outer ring and the inner ring. When such locking occurs in the one-way clutch, the alternator and the engine are directly coupled as if no one-way clutch were used. The tension of the driving belt is frequently and repeatedly changed as described above. As a result, the life of the driving belt is shortened.